Fig.4. Analysis of crystalline mat and commercially available calcium carbonate by infrared (IR) spectrometry. The infrared spectra were obtained for the crystalline mat (red line) and commercially available calcium carbonate (black line). The graph shows transmittance (arbitrary units) at each wavenumber. By comparing the IR spectra obtained in this study with those of calcium carbonate polymorphs obtained in previous studies (Adler and Kerr, 1962; Kikuchi and Tamiya, 1984), the crystalline mat was determined to be aragonite, whereas, the commercially available calcium carbonate was determined to be a mixture of aragonite and calcite, accounting for the wide and double headed V₃ band. The peaks in transmittance are due primarily to the CO₃^2- radical of calcium carbonate. V₃, the characteristic transmittance peak for calcium carbonate, represents doubly degenerate asymmetric stretching of the CO₃^2- radical. V₂ corresponds to out-of-plane bending and V₄ to doubly degenerate planular bending. Both sample have other notable peaks (asterisk) found in the spectra of aragonite. The peak in the range of approximately 3250–3750 wavenumbercm^-1 is due to the presence of water (H₂O) in the samples.